Abstract:
In the monoclinic polytype NbS$_3$-II, the monoclinic ${\mathbf b}$-axis of which coincides with the direction of greatest conductivity, two charge density waves (CDWs) have been observed at room temperature: CDW-0 with the wave vector ${\mathbf q}_0 = 0.5{\mathbf a}^* + 0.352{\mathbf b}^* + 0.5{\mathbf c}^*$ and CDW-1 with the wave vector ${\mathbf q}_1 = 0.5{\mathbf a}^* + 0.298{\mathbf b}^* + 0.5{\mathbf c}^*$. X-ray diffraction patterns obtained in the temperature range of $90$–$500$ K have shown that the vectors ${\mathbf q}_0$ and ${\mathbf q}_1$ depend on the temperature, but their ${\mathbf b}^*$ coordinates satisfy the relation $2q_{0}^{{{\mathbf{b}}\text{*}}}(T) + q_{1}^{{{\mathbf{b}}\text{*}}}(T) = {\text{const}} = 1$ . It has been concluded that the wave vector ${\mathbf q}_1$ of CDW-1 is determined not only by the nesting of Fermi surfaces, but also by the vector ${\mathbf q}_0$, because CDW-1 is adjusted to the second harmonic of CDW-0, which indicates the interaction between charge density waves. This conclusion has been confirmed by structural studies of NbS$_3$-II samples, the lattice of which is strongly deformed due to a high concentration of twins. In these samples, CDW-0 is conserved, and the wave vector of CDW-1 has the ${\mathbf b}^*$ component not related to ${\mathbf q}_0$.
Fulltext:
PDF file (461 kB)
First page:
PDF file